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| United States Patent |
5,348,665
|
|
Schulte
, et al.
|
September 20, 1994
|
Method for the degradation of harmful substances in water by means of
hydrogen peroxide under UV irradiation
Abstract
The degradation of harmful substances in water by compounds, such as
hydrogen peroxide, which form hydroxyl radicals under UV irradiation in
continuous reactors is improved when the irradiation is carried out in a
reactor with a specific reactor volume of at least 10 liters per kW of the
UV radiator or radiators, and if the amount of water to be treated is 0.25
to 25 times the amount of the intrinsic volume of the reactor flows
through the reactor per hour. It is particularly preferred that the water
volume per hour to be treated is 0.25 to 10 times the intrinsic reactor
volume.
| Inventors:
|
Schulte; Peter (Alzenau-Hoerstein, DE);
Volkmer; Michael (Hanau, DE);
Kuhn; Frank (Gelhausen, DE)
|
| Assignee:
|
Degussa Aktiengesellschaft (Frankfurt am Main, DE)
|
| Appl. No.:
|
979538 |
| Filed:
|
November 20, 1992 |
Foreign Application Priority Data
| Current U.S. Class: |
210/748; 210/759; 210/763; 588/309; 588/320; 588/409 |
| Intern'l Class: |
C02F 001/30; C02F 001/72 |
| Field of Search: |
210/192,748,758,759,763
588/212,219,222,227,243,247
423/29,DIG. 20
|
References Cited
U.S. Patent Documents
| 2648774 | Aug., 1953 | Whitlock | 250/43.
|
| 3924139 | Dec., 1975 | Hirose et al. | 210/199.
|
| 4012321 | Mar., 1977 | Koubek | 210/63.
|
| 4204956 | May., 1980 | Flatow | 210/192.
|
| 4446029 | May., 1984 | Bertermier et al. | 210/748.
|
| 4792407 | Dec., 1988 | Zeff et al. | 210/748.
|
| 4793931 | Dec., 1988 | Stevens et al. | 210/636.
|
| 4849114 | Jul., 1989 | Zeff et al. | 210/748.
|
| 4861484 | Aug., 1989 | Lichtin et al. | 210/748.
|
| 4952376 | Aug., 1990 | Peterson et al. | 422/186.
|
| 5043080 | Aug., 1991 | Cater et al. | 210/748.
|
| Foreign Patent Documents |
| 0436922 | Jul., 1991 | EP.
| |
| 2300273 | Jul., 1973 | DE.
| |
| 3836850 | May., 1990 | DE.
| |
| 1-258794 | Oct., 1989 | JP.
| |
Other References
German Gebrauchsmuster 90 17 684.7 to IBL Umwelt dated Jan. 2, 1992.
"Labortechnik und Arbeitsmethoden in der Photochemie".
Ullmanns Encyklopaedie der technishen Chemie, "Apparate fuer
Lichtreaktionen," by Dr. Balke et al., (1951), p. 765.
G. O. Schenck, "Apparate fuer Lichtreaktionen und ihre Anwendung in der
praeparativen Photochemie," pp. 105, 108 and 109.
N. Clarke et al., "High Purity Water Using H.sub.2 O.sub.2 and UV
Radiation," Effluent and Water Treatment Journal, Sep. 1982, pp. 335-341.
An advertizement by Peroxidation Systems, Inc. Perox-Pure Modular Treatment
Services.
M. Malaiyandi et al., 2406 Water Research, vol. 14 (1980), No. 8, Oxford,
Great Britain.
Patent Abstracts of Japan, Author Unknown, C-675, Jan. 16, 1990, vol. 14,
No. 17, Abstract No. 1-258794.
"Chemische bzw. photochemische Oxidationsverfahren zur Entfernung
organischer Bestandteile aus Abwaessern," D. Ott, 1989, pp. 134-158
"Wasserkalender".
|
Primary Examiner: Nessler; Cynthia L.
Attorney, Agent or Firm: Beveridge, DeGrandi, Weilacher & Young
Claims
We claim:
1. A method for degradation of a harmful substance in water, comprising:
adding to the water a sufficient amount of a compound which provides a
source of hydroxyl radicals under UV irradiation for performing a desired
degree of degradation; passing the water and compound through a continuous
flow reactor; irradiating the water and compound in the reactor with UV
radiation from at least one UV radiator, such that a ratio of the
non-irradiated volume to the irradiated volume, as determined at a
wavelength of 265 nm, is greater than 2, wherein the reactor has a
specific reactor volume of at least 40 liters per kW of electric power of
the at least one UV radiator and wherein an amount of water is treated per
hour which is equivalent to 0.5 to 5 times an intrinsic volume of the
reactor.
2. The method according to claim 1, wherein the specific reactor volume is
40 to 100 l/kW.
3. The method according to claim 1, wherein the amount of water treated per
hour is 0.75 to 2 times the intrinsic volume of the reactor.
4. The method according to claim 1, wherein during the passing step, the
water to be treated flows through several reactors connected in series.
5. The method according to claim 1, wherein the water to be treated
contains formaldehyde as the harmful substance.
6. The method according to claim 1, wherein the UV radiator is a
polychromatic radiation source having a wavelength in the range of
approximately 185 to 400 nm.
7. The method according to claim 1, wherein the compound is selected from
the group consisting of: hydrogen peroxide, sodium percarbonate, sodium
perborate and peroxycarboxylic acids.
8. The method according to claim 1, further comprising:
adding a transitional metal catalyst to the water to be treated to support
oxidation of the harmful substance with the compound.
9. The method according to claim 8, wherein the catalyst is an iron
compound.
10. The method according to claim 8, wherein the compound is hydrogen
peroxide.
11. A method for degradation of a harmful substance in water, comprising:
adding a sufficient quantity of hydrogen peroxide to the water, wherein the
hydrogen peroxide provides a source of hydroxyl radicals, so as to achieve
a desired degree of degradation of the harmful substance contained in the
water;
passing the water and hydrogen peroxide through a reaction zone;
irradiating the water and hydrogen peroxide in the reaction zone with
ultraviolet radiation from at least one ultraviolet radiator, such that
the hydrogen peroxide forms hydroxyl radicals which oxidize the harmful
substance in the water, and wherein a ratio of the non-irradiated volume
to the irradiated volume, as determined at a wavelength of 265 nm, is
greater than 2;
wherein the reaction zone has a specific volume of at least 40 liters per
kilowatt of electric power of the at least one ultraviolet radiator, and
wherein an amount of water treated per hour is equivalent to 0.5 to 5
times an intrinsic volume of the reaction zone.
12. The method according to claim 11, wherein the specific volume of the
reaction zone is in the range of 40 to 100 l/kW.
13. The method according to claim 11, wherein the amount of water treated
per hour is 0.75 to 2 times the intrinsic volume of the reaction zone.
14. The method according to claim 11, wherein during the passing step, the
water to be treated flows through several reactors connected in series.
15. The method according to claim 11, further comprising:
adding an iron containing compound to the water as a catalyst to support
oxidation of the harmful substance.
Description
BACKGROUND OF THE INVENTION
This invention relates to a method for the degradation of harmful
substances, such as pollutants or contaminants, in water by means of
compounds which form hydroxyl radicals, especially hydrogen peroxide,
under UV irradiation. It is particularly preferred that the UV radiation
is polychromatic radiation having a wavelength in the range of
approximately 185 to 400 nm. Furthermore, the reaction may take place in a
continuous flow reactor, through which the polluted or contaminated water
flows, along with a sufficient amount of hydrogen peroxide.
U.S. Pat. No. 4,012,321; U.S. Pat. No. 4,446,029; German Patent Appl. No.
38 36 850 A; and D. Otto in "Wasserkalender," 1989 pp 134-158 show that
the oxidation action of hydrogen peroxide can be vigorously increased if
it is irradiated in an aqueous solution with monochromatic or
polychromatic ultraviolet radiation. All of these references are entirely
incorporated herein by reference. As a result of the UV irradiation,
hydrogen peroxide decomposes into hydroxyl radicals and the harmful
substances contained in the water are degraded by this strong oxidation
agent. This treatment method is suitable for the degradation of families
of compounds (classes of substances) which are chemically very different,
such as hydrocarbons, alcohols, ethers, acids, aldehydes, ketones, amino
compounds, halogen compounds, and cyanides. Typically, mercury
low-pressure radiators are used as a radiation source for monochromatic
radiation having wavelengths of, e.g., 185, 254 and 265 nm. Medium or
high-pressure radiators are used for producing polychromatic radiation
with a wavelength spectrum in the range of, e.g., 185 to 400 nm. To the
extent it is desired, the oxidation action of the H.sub.2 O.sub.2 /UV
irradiation system can be further increased by means of the addition of
transitional metal ions, especially iron ions. This is described in U.S.
Pat. No. 5,043,080, which patent is entirely incorporated by reference.
The treatment of water containing harmful substances with H.sub.2 O.sub.2
/UV radiation takes place on an industrial scale in continuous reactors.
In the case of a low load of harmful substances, or in the case of readily
degradable substances, a single passage of the water compounded with
hydrogen peroxide through the irradiated reactor can be sufficient. A high
load of harmful substances requires a process with reflux or recycle. It
is known that the penetration depth of the radiation into the solution to
be treated is only a few millimeters to a few centimeters. The penetration
depth is a function of the wavelength of the radiation and the
concentration of hydrogen peroxide and harmful substances in the water.
It is generally believed that, in order to achieve a satisfactory action,
taking into consideration the indicated absorption behavior, the layers of
liquid close to the radiator would have to be constantly renewed, and
thus, the entire amount of liquid would have to be exposed to the
short-wave radiation. To this end, the solution to be treated is pumped in
a continuous manner at high speed through one or several continuous UV
reactors connected in series. Typically, these UV reactors are tubular
shaped. In the method of German Patent Appl. No. 38 36 850 A1, for
example, reactors with a total layer thickness of irradiated solution of
1.65 to 12.5 cm are used, and the flow speed in the smallest section is
adjusted to at least 0.2 m/sec. In the method of European Patent Appl. No.
0,436,922 A2 (which is also entirely incorporated herein by reference),
tubular reactors are arranged around the radiation source. These tubular
reactors have a radial layer thickness in the range of 0.1 to 50 mm.
In commercial tubular UV reactors, their specific volume is usually in the
range of 1 to 10 liters per kilowatt (kW) of the electric power wattage of
the radiator(s). The liquid flowthrough per hour should always be as high
as possible, according to the data of the manufacturer, in order to
achieve an ideal intermixing. Generally, the flowthrough rate is
approximately 20 to 50 times the volume of the UV reactor.
A disadvantage of the previously known methods and commercial reactors is
the requirement of having to use technically expensive and complicated UV
reactors. In addition, the systems must be designed in such a manner that
they can be operated with a high flowthrough rate, which further increases
the necessary volume of capital. There was also interest in improving the
rate of degradation of the harmful substances in water at a given
performance (i.e., power, wattage) of the UV radiator (s) and with as low
an outlay for equipment as possible.
BRIEF DESCRIPTION OF THE INVENTION
It is one objective of the invention to overcome these and other
deficiencies in the known treatment processes.
In the method in accordance with the invention, the degradation of harmful
substances in water includes adding to the water a sufficient amount of a
compound which forms hydroxyl radicals under UV irradiation so as to
perform a desired degree of degradation. Preferably, this compound is
hydrogen peroxide. The water and compound are passed through a reaction
zone, such as a continuous flow reactor and irradiated therein with UV
radiation from at least one UV radiator. In the method in accordance with
the invention, the reactor has a specific volume of at least 10 liters per
kW of electric power of the UV radiator or radiators. Furthermore, in the
method, an amount of water is treated per hour which is equivalent to 0.25
to 25 times an intrinsic volume of the reactor.
According to the preferred embodiments of the method of the invention, the
specific reactor volume is 20 to 200 l/kW. 40 to 100 l/kW is particularly
preferred. The amount of water to be treated per hour is preferably 0.25
to 10 times the amount of the intrinsic volume of the reactor. It is even
more preferable if the hourly water flow is 0.5 to 5 times the intrinsic
reactor volume, and 0.75 to 2 times the intrinsic reactor volume is
particularly preferred. In order to increase the capacity and/or the rate
of degradation of harmful substances, several UV reactors can be connected
in series in a known manner.
In another aspect of the invention, a transitional metal catalyst may be
added to the water to be treated. This catalyst supports oxidation of the
harmful substances with the compound. Preferably, the catalyst is an iron
compound.
In one preferred embodiment of the invention, the UV radiator is a
polychromatic radiation source having a wavelength in the range of
approximately 185 to 400 nm.
Additionally, the method in accordance with the invention may be carried
out such that the irradiation takes place in a reactor, wherein the ratio
of the non-irradiated volume to the irradiated volume, as determined by
the penetration depth of radiation at a wavelength of 265 nm, is greater
than 1.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in conjunction with the attached Figures,
wherein:
FIG. 1 which shows a schematic diagram of a reactor system such as that
used in Example 1;
FIG. 2 which shows a schematic diagram of a reactor system in accordance
with the invention; and
FIG. 3 which shows a schematic diagram of another reactor system in
accordance with the invention. The figures are schematic representations
of reactor systems such as those used in the process in accordance with
the invention. The figures are not intended to be drawn to scale. They
should be considered as illustrative of the invention, and not limiting
the same.
DETAILED DESCRIPTION OF THE INVENTION
The method in accordance with the invention will be described in the
detailed description which follows. Specific examples also follow which
are intended to illustrate the method of the invention. These examples
should be construed as being illustrative of the invention, and not
limiting the same.
In principle, the method in accordance with the invention can be carried
out with UV rays from a monochromatic or polychromatic radiation source;
however, radiators with polychromatic radiation having an ultraviolet
spectrum in the range of 185 to 400 nm are preferred. The entire spectrum
of UV high-pressure radiators generally also sweeps over so as to include
a portion of the visible light spectrum. In the case of polychromatic
radiation from medium and high pressure radiators, it is surprising that
no additional apparatus is required to elevate the turbulence in order to
achieve a thorough intermixing of the reactor contents. A sufficient
intermixing is achieved by the development of the heat from such
radiators. The heating itself supports the degradation of harmful
substances.
It is advantageous if the reactors used in accordance with the invention
are cylindrical with the irradiated reactor volume to be associated with
each radiator being considerably smaller than the total volume to be
associated with the radiator (i.e., the reactor volume per radiator). The
reactor, which can comprise one or several radiators in different
arrangements, is therefore distinguished in that irradiated and
non-irradiated volume components are present in it adjacent to each other.
The ratio of the non-irradiated to the irradiated volume, determined by
the penetration depth at a wavelength of 265 nm, is greater than 1 and
preferably greater than 2. It is particularly preferred if this ratio is
greater than 5. In the case of an axial arrangement of a radiator in a
cylindrical container, the radius of the reactor is considerably greater
than the penetration depth of the radiation. In this way, no expensive
reactor design is necessary; but rather, the radiators can be built into
customary containers. In addition, devices for circulating the reactor
contents, as well as apparatuses for recirculation between a UV reactor
and a receiver container or a post reaction container are rendered
superfluous. The output of the pumps is merely adapted to the desired
capacity.
Although not wishing to be bound by any particular theory of operation, it
is believed that the increase of the degradation rate comes about because
several reactions take place in parallel in the reactor in the method of
the invention. These reactions include: (a) the photoreaction under
formation of the reactive hydroxyl radicals; (b) the conversion reaction
of the hydroxyl radicals with the harmful substances; (c) the conversion
of molecules of the harmful substances activated by UV absorption with
hydrogen peroxide; and (d) the oxidation of side products obtained from
the conversion according to reactions (b) and (c) with H.sub.2 O.sub.2 or
OH radicals. The available radiator performance is better utilized.
The method of the invention is suitable for the degradation of chemically
different compounds containing carbon, such as those already mentioned in
the Background section of this application. Formaldehyde can be degraded
particularly well, wherein, as is apparent from the reference examples
which follow, degradation was not satisfactory and/or a rather significant
expense was involved in the state of the art processes.
The pH in the solution to be treated is adapted to the harmful substances
contained in the solution by the addition of acids or bases. The pH is
frequently in the acidic pH range; however, a pH in the range of 8-11 is
customary, for example, in the degradation of complex cyanides.
The water to be treated which is flowing through the UV reactor contains
hydrogen peroxide in an effective amount so as to degradate the harmful
substances. The dosing of hydrogen peroxide takes place in a known manner
by means of aqueous solutions with a content between 0.3 and 85% H.sub.2
O.sub.2 by weight, especially 30 to 75% H.sub.2 O.sub.2 by weight, with
the amount depending on the harmful substance content and the desired
degradation of the harmful substances. Those skilled in the art will
easily determine the optimum amount of H.sub.2 O.sub.2 by an orienting
test. Instead of H.sub.2 O.sub.2, compounds can also be used which split
off H.sub.2 O.sub.2 in aqueous solution. Examples of such compounds are
sodium percarbonate or sodium perborate. Compounds can also be used which
form OH radicals themselves under UV irradiation, such as,
peroxycarboxylic acids.
The temperature during the H.sub.2 O.sub.2 /UV treatment may range from
approximately 5.degree. C. to approximately 95.degree. C., with the range
of 20.degree. to 90.degree. C. being especially preferred. In the case of
substances which are difficult to degrade, a treatment at elevated
temperatures, such as, 50.degree. to 80.degree. C. is usually
advantageous. If medium and high-pressure radiators are used, too much
warming can occur, for example, in the case of a high energy charge with a
low flowthrough rate, such that cooling measures are required in order to
maintain the temperature below 95.degree. C. It is preferred that the
temperature be kept below 90.degree. C. In the case of low-pressure
radiators, it is necessary, as a rule, to maintain the temperature
constant in the range of 5.degree. to 30.degree. C.
The method of the invention also includes the co-use of catalytically
active transition metal ions as a catalyst, particularly iron (Fe) ions.
This catalyst supports the oxidation of the harmful substances. The
H.sub.2 O.sub.2 /UV/Fe ion system exhibits, as is known, a synergistic
effect as compared to the H.sub.2 O.sub.2 /UV and the H.sub.2 O.sub.2 /Fe
ion systems. However, as a rule, the H.sub.2 O.sub.2 /UV/Fe ion system
makes it necessary to include a separating device for separating the
resulting iron hydroxide sludges, as well as measures for the return of Fe
ions or the removal of the sludges.
Those skilled in the art would not have expected that an improved method
for the degradation of harmful substances with reduced equipment outlay
was able to be achieved in the method in accordance with the invention.
Particularly, it is unexpected that by the enlargement of the specific
reactor volume and enlargement of the ratio of the non-irradiated to the
irradiated volume and lowering of the flowthrough, improved results in
accordance with the invention could be achieved.
The invention will be described in more detail by the following examples
and reference examples.
EXAMPLES 1 TO 4
These Examples relate to the degradation of formaldehyde in a water,
additionally containing formic acid, with hydrogen peroxide under UV
irradiation. In these Examples, the UV radiation source was a
high-pressure lamp, type: DQ 1023 of the firm W. C. Heraeus GmbH, Hanau,
Germany. The degradation of harmful substances takes place in variously
dimensioned, cylindrical UV reactors, while varying the flowthrough rate.
The conditions were as follows: (a) Formaldehyde concentration: 1.3 g/l;
(b) H.sub.2 O.sub.2 addition: up to a concentration of 3.0 g/l; (c)
electric power of the radiator: 1 kW; (d) pH: adjustment with formic acid
to 3.0; and (e) reaction temperature: approximately 25.degree. C. The
tests took place in a batch method with a 600 liter specimen in each
instance. The particular UV reactor was tied into a loop including a 600
liter storage container with the solution to be treated, and, in addition
to the UV reactor, a circulation pump and the loop line in Examples 1 to
3. The treatment time was 60 minutes.
The physical characteristics of Reactor A are as follows:
Height: 80 cm; diameter: 10 cm; volume (less the volume of the UV lamp): 4
liters; arrangement of the lamp: axial.
FIG. 1 shows a schematic drawing of a reactor system such as that of
Reactor A. The water to be treated is stored in a 600 liter storage tank
10. A circulation pump 12 pumps the water to be treated into the reactor
14. The ultraviolet light source 16 is arranged axially to the direction
of flow with respect to the cylindrical axis of the reactor 14. The UV
radiator 16 is shown in reactor 14 in FIG. 1. After the water is
irradiated and flows through the reactor 14, it is recirculated into the
storage tank 10 and after treatment, discharged via the discharge pipe 18.
In the reactor systems in accordance with the invention, the UV light
source may be integrated into the wall of the reactor in a conventional
container, or the reactor may be made of an ultraviolet transmissive
material, wherein the UV source is independent from the reactor.
The physical characteristics of Reactor B are as follows:
Height: 200 cm; diameter: 30 cm; filling volume: 120 liters; arrangement of
the lamp: obliquely to the flow; inflow: at the lower end of the reactor;
discharge: at the upper end of the reactor.
FIG. 2 shows a schematic diagram of a reactor system such as the one used
for Reactor B. In this schematic, the water to be treated is stored in a
600 liter storage tank 20. The water to be treated is pumped from the tank
20 to the reactor 24 via a circulation pump 22. The water enters the
reactor 24 at the bottom and is irradiated by UV radiation sources 26
arranged obliquely to the direction of flow. One or more UV radiation
sources 26 may be used, for example, four are shown in FIG. 2. The treated
water exits the top of the reactor 24 through discharge pipe 28.
FIG. 2 also shows an recirculation loop 30, wherein the water may be
recirculated to the tank 20 for further treatment. The finally treated
water is discharged for further processing or disposal through pipe 32.
The physical characteristics of Reactor C are as follows:
Height: 150 cm; diameter: 120 cm; volume: 1700 liters; arrangement of the
lamp: axial; inflow and discharge: through opposite connection pieces at
the cylindrical wall; filling height during operation: 53 cm (=600
liters). The loop of the test arrangement in Example 4 did not contain a
storage container.
FIG. 3 shows a schematic diagram of a reactor system such as that used in
Reactor C. A storage container 40 is shown, although, as noted above, the
arrangement of Example 4 did not include the storage container 40. Those
skilled in the art will recognize that the water for treatment may be
introduced into the reactor system directly from a previous process,
without the need for a storage container. A circulation pump 42 introduces
the water to be treated into the bottom of the reactor 44. The treated
water exits the reactor 44 through a discharge pipe 46 at the opposite
side and at the bottom of the reactor 44. As also mentioned above, the
reactor 44 is only partially filled with water 48 during operation of the
system. Ultraviolet radiation source(s) 50 are arranged in the axial
direction with respect the cylindrical axis of the reactor 44. As an
example, in the system of FIG. 3, three ultraviolet radiation sources 50
are shown, although more or less may be used.
The results of the treatment process and the test data using Reactors A, B
and C are shown below in Table 1.
TABLE 1
__________________________________________________________________________
Spec. Reactor
Flow- H.sub.2 O.sub.2 **
CH.sub.2 O***
Example Volume through Degradation
Degradation
No. Reactor
liters per kW
liter/h (RV/h)*
mg per liter
mg per liter
__________________________________________________________________________
1 A 4 600 325 95
(150)
2 B 120 8500 170 105
(70.8)
3 B 600 385 125
(5.0)
4 C 600 600 500 260
(1)
__________________________________________________________________________
*RV = Reactor Volumes
**Determination by the Cerium
Determination of content after end of test
(IV) Sulfate Method using a specimen from the 600 liter
***Determination by the Sulfite Method
storage container or the 600 l reactor
Note: The work was performed in analogy to Example 1, at 70.degree. C.
and 2 kW radiator
power at a flow through of 2.5 or 0.4 m.sup.3 /h. The formaldehyde
degradation was 10
and 20%.
The cerium (IV) sulfate method for determining hydrogen peroxide
degradation and the sulfite method for determining CH.sub.2 O
(formaldehyde) degradation are well known to those skilled in the art.
Example 1 is not in accordance with the invention with regard to the
specific reactor volume and also the flowthrough rate. Example 2 is not in
accordance with the invention with regard to the flowthrough rate. In
Example 3, which is in accordance with the invention, the degradation of
formaldehyde was increased over that in Example 2 by approximately 19% and
by 32% over Example 1. The significant influence of the enlarged specific
volume follows from a comparison of Examples 3 and 4.
EXAMPLES 5 AND 6
The waste water treatment in these Examples takes place in the loop system
according to Examples 2 and 3, that is, with reactor B, but with 3 UV
radiators of 1 kW electric power each. The radiator arrangement is oblique
to the flow. Treatment time is 2 hours. The formaldehyde content of the
600 liter batch at the start was 1.3 g/l, the H.sub.2 O.sub.2 content at
the start was 3.0 g/l, and the pH was 3. The results are shown in Table 2.
The H.sub.2 O.sub.2 content and the CH.sub.2 O content are determined from
a specimen from the storage container, removed after the end of the test.
TABLE 2
______________________________________
Example
Flowthrough
H.sub.2 O.sub.2 degradation
CH.sub.2 O degradation
No. 1 l/h mg/l mg/l
______________________________________
5 8500 (70.8)
1050 460
6 300 (2.0) 1710 680
______________________________________
Example 5 is not in accordance with the invention. The degradation of
formaldehyde was increased over Example 5 by approximately 50% by reducing
the flowthrough in Example 6.
EXAMPLES 7 TO 9
The degradation of formaldehyde in a continuous process with a capacity of
400 liter/h was investigated. The following equipment systems formed the
base for these examples:
Example 7
Small UV reactor (length: 77 cm; diameter: 8 cm; effective volume: 3.5
liters); UV high-pressure radiator, 2 kW electric power. Direct passage
with 400 liters/h from a storage container with 600 liters of the water
compounded with H.sub.2 O.sub.2 to be treated. Determination of CH.sub.2 O
after the water has left the UV reactor.
Example 8
UV reactor according to Example 7, tied into a loop including the reactor,
a non-irradiated storage container, a loop line and a pump. 400 liters/h
of water to be treated was supplied in a continuous manner to the storage
container with 600 liters of water to be treated and the equivalent amount
of treated water was removed. Flowthrough in the loop was 10 m.sup.3 /h.
Example 9
The storage container of Example 8 with the same degree of filling (600
liters) and the same 2 kW radiator served as the UV reactor; inflow and
outflow from the 600 liter UV reactor were 400 l/h each. The water to be
treated in the examples was process water from a polyol production. This
water contained formaldehyde, formic acid, formate, methanol and had a pH
of 2.5 to 2.8 and a temperature of 60.degree. to 70.degree. C. Prior to
entrance into the reactor (examples 7, 9) and into the storage container
(example 8), 2.0 g H.sub.2 O.sub.2 (as 50% by weight aqueous solution) per
liter water were added. The degradation rate (% formaldehyde) was
determined in the treated water removed.
TABLE 3
______________________________________
Exam- CH.sub.2 O
Temper-
ple Inflow Outflow degradation
ature
No. CH.sub.2 O
H.sub.2 O.sub.2
CH.sub.2 O
H.sub.2 O.sub.2
rate % .degree.C.
______________________________________
7 1.30 2.0 1.05 1.55 20 66.fwdarw.69
8 0.95 2.0 0.65 1.60 32 71.fwdarw.72
9 1.0 2.0 0.40 0.70 60 60.fwdarw.58
______________________________________
The degradation rate was able to be increased by over 50% by means of the
combination of the non-inventive reactor (Example 7) with an irradiated
reactor and loop arrangement (Example 8, also not in accordance with the
invention); however a degradation rate three times greater is achieved in
Example 9, which is in accordance with the invention.
EXAMPLE 10
Process waste water with the following composition was treated in a
continuous manner with H.sub.2 O.sub.2 under UV irradiation in accordance
with the invention in a reactor with a diameter of 60 cm and a volume of
600 liters. The flowthrough, the amount of H.sub.2 O.sub.2 and the energy
charge (1-5 high-pressure radiators, 2 kW each, type DQ 2023 of the firm
W. C. Heraeus GmbH, Hanau) were varied. Composition of the water:
approximately 1.6 g/l formaldehyde, approximately 1.8 g/l formic acid, 0.5
g/l methanol, 0.01 g/l calcium formate; CSB value approximately 3.5 g/l.
The results follow from Tables 4 to 6.
TABLE 4
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Formaldehyde degradation as a function of the flowthrough
and the irradiation of energy at an initial concentration of
H.sub.2 O.sub.2 of 2 g H.sub.2 O.sub.2 /l process waste water
Flowthrough Formaldehyde degradation (%)
(m.sup.3 /kh)
0 kW 2 kW 6 kW 10 kW
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0.4 10 60 74 74
0.6 10 52 58 69
0.8 10 35 50 62
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TABLE 5
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Rate of formaldehyde degradation (%) at 0.4 m.sup.3 /h
flowthrough, 3 .times. 2 kW HD radiator as a function of the
concentration of H.sub.2 O.sub.2.
H.sub.2 O.sub.2 concentration
CH.sub.2 O degradation
(g/l) (%)
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1.0 50
2.0 73
3.0 81
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TABLE 6
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Connecting 2 reactors in series: (volume of each: 600 liters;
diameter: 60 cm and 100 cm). Formaldehyde degradation rate as a
function of the flowthrough; H.sub.2 O.sub.2 concentration: 2 g/l; a 5
.times. 2
kW radiator in each of the reactors (Reactor 1 and Reactor 2).
Flowthrough
CH.sub.2 O degradation (%)
Temperature
(m.sup.3 /h)
after Reactor 1
after Reactor 2
(.degree.C.)
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0.8 61 75 70.fwdarw.93
1.2 57 71 72.fwdarw.88
1.6 43 58 69.fwdarw.82
______________________________________
EXAMPLE 11
Example 10 was repeated using a reactor with a diameter of 100 cm.
Essentially the same results as in Example 10, Tables 4 and 5, resulted.
While the invention has been described in terms of various specific
examples, those skilled in this art will recognize that various
modifications and changes can be made without departing from the spirit
and scope of the invention, as defined in the claims.
The priority document, German Patent Application No. P 41 38 421.0, filed
in Germany on Nov. 22, 1991, is relied on and entirely incorporated herein
by reference.
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